Ransomware is computer malware that installs covertly on a victim's computer, executes a cryptovirology attack that adversely affects the victim's computer, and demands a ransom payment to restore the victim's computer to its former state. Simple ransomware may lock the victim's computer in a way which is not difficult for a knowledgeable person to reverse, and display a message requesting payment to unlock it. More advanced malware encrypts the victim's files, making them inaccessible, and demands a ransom payment to decrypt them. The ransomware may also encrypt the computer's Master File Table (MFT) or the entire hard drive. Thus, ransomware is a denial-of-access attack that prevents computer users from accessing files without employing a brute-force attack since it is generally impossible to decrypt the files without the decryption key. Ransomware attacks are typically carried out using a Trojan that has a payload disguised as a legitimate file.